Turkish President Recep Tayyip Erdogan on Sunday declared victory in a tightly-contested presidential election, extending his 15-year grip on power in the face of a revitalised opposition.

Turkish voters had for the first time cast ballots for both president and parliament in the snap polls, with Erdogan looking for a first-round knockout and an overall majority for his ruling Justice and Development Party (AKP).

The stakes in this election are particularly high as the new president is the first to enjoy enhanced powers under a new constitution agreed in an April 2017 referendum strongly backed by Erdogan.

Erdogan was on course to defeat his nearest rival Muharrem Ince with more than half the vote without needing a second round, initial results showed.

“The unofficial results of the elections have become clear. According to these... I have been entrusted by the nation with the task and duties of the presidency,” Erdogan said at his Istanbul residence.

He added that the alliance led by the AKP had won the majority in parliament.

Erdogan has just under 53 per cent in the presidential poll while Ince, of the secular Republican People's Party (CHP), was on 31 per cent, state-run Anadolu news agency said, based on a 96 per cent vote count. The figures could yet change as final ballot boxes are opened.

But celebrations were already beginning outside Erdogan's residence in Istanbul and AKP headquarters in Ankara, with crowds of flag-waving supporters, AFP correspondents said.

Trailing were Meral Aksener of the nationalist (Iyi) Good Party with over 7 per cent and Selahattin Demirtas of the pro-Kurdish Peoples' Democratic Party (HDP) with almost eight per cent.

A count of almost over 95 per cent for the parliamentary election also showed that Erdogan's AKP — along with its Nationalist Movement Party (MHP) allies — were well ahead and set for an overall majority.

The pro-Kurdish Peoples' Democratic Party (HDP) was polling 11 per cent, well over the 10 per cent minimum threshold needed to win 46 seats, which would make it the second largest opposition party in the new chamber.

Turnout in the presidential election was almost 88 percent, according to the figures published by Anadolu.

'Protect your rights'

Erdogan had faced an energetic campaign by Ince, who has rivalled the incumbent's charisma and crowd-pulling on the campaign trail, as well as a strong opposition alliance in the legislative poll.

Ince vowed to spend the night at the headquarters of Turkey's election authority in Ankara to ensure a fair count and urged supporters to stay in polling stations until the final vote was counted.

The CHP said it had recorded violations in particular in the southeastern province of Sanliurfa, although Erdogan insisted, after voting himself, there was no major problem.

“I will protect your rights. All we want is a fair competition. Have no fear and don't believe in demoralising reports,” Ince said after polls closed.

Several world leaders supportive of Erdogan, including Azerbaijani President Ilham Aliyev and Qatari Emir Tamim bin Hamad Al-Thani, called to congratulate him on his “victory”, the presidency said.